GISdevelopment.net --> Application --> Geology
Chang-Uk Hyun
Department of Civil, Urban and Geosystem Engineering, Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
hyuncu99@snu.ac.kr
Hyeong-Dong Park
Department of Civil, Urban and Geosystem Engineering, Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
hpark@snu.ac.kr
Abstract Combinations of reflectance spectroscopy and various constituents matching algorithms have been successfully used to classify and to detect geomaterials in field of remote sensing. Measuring reflectance spectra on the rock surface can be applied to assess degradation of rock surface as a new non-destructive inspection method. In this paper the spectral reflectances of weathered granite specimens of Mt. Gwanak were measured by using field spectrometer and spectral characteristics of reference minerals were used to identify rock-forming minerals of the granite from the spectral reflectances obtained using field spectrometer. Granite is mainly composed of quartz, feldspar and mica. Hardness and durability of quartz are greater than other granite forming minerals and quartz has no diagnostic peak in spectral reflectance curves, but feldspar and mica produce clay minerals, such as illite and kaolinite, according to weathering processes. Thus comparison of the amount of the clay minerals using absorption peak in the spectral reflectance curves among differently weathered granite specimens could result in newly designed weathering indices against rock surface mineral composition.
1. Introduction
In civil engineering, rocks are used for building materials and foundation of construction, so its engineering properties and physical characteristics are critical for concrete construction. Weathering changes physical characteristics of rocks, such as strength, hardness and durability, or texture and color on the surface which are important for conservation of stone monument and exterior of the building. To assess weathering degree of rocks various techniques and methods have been used. Qualitative assessments using naked eye of geologist and chemical analyses of rock-forming mineral composition have been commonly used to assess rock deterioration. But chemical analyses are time-consuming and damage objects. The assessments by geologist have limits to produce subjective and qualitative results. Reflectance spectroscopy is non-destructive and makes fast investigation on the rock surface. Spectra measured using spectrometer on the rock surface make researcher quantitative interpretation about weathering degree. In this paper we investigated weathering processes of granite forming minerals and measured reflectance curves on the weathered granite specimens of Mt. Gwanak in Korea. By using absorption features of the spectra weathering degree of specimens could be compared.
2. Weathering Characteristics of Mt. Gwanak Granite
Granite of Mt. Gwanak is biotite granite (Kwon et al., 1995). Its constituents are quartz, feldspar and mica, especially biotite. Hardness and durability of quartz are greater than other granite forming minerals and quartz has no diagnostic peak in spectral reflectance curves. Feldspar and mica produce clay minerals, such as illite and kaolinite, according to weathering processes. Spectral reflectance curves of granite constituents have no diagnostic absorption peaks except for microcline in the vicinity of 2.2? wavelength. Spectral reflectance curves of clay minerals show strong absorption peak in the vicinity of 2.2? wavelength (Clark et al., 2003).
3. Surface Weathering Degree Assessment of Granite
Field spectrometer (Fieldspec®3) was used to measure surface reflectance curves of granite specimens. The prove of 25 degree FOV (field of view) was applied to measure reflectances of three specimens and two types of target area, circles of 1cm and 2cm diameter, were set up (Fig. 1).
Fig. 1. Target areas for measurement of spectral reflectances. The diameter of big spot is about 2cm and the diameter of small spot is about 1cm.
4. Results
Spectral reflectances of weathered granite surface were measured and continuum removal step was processed (Fig. 2) to remove background absorptions and extract inherent absorption features (Clark and Roush, 1984; Kruse et al., 1985). Quantitative comparison among weathered specimens was derived using absorption feature and its depth of 2.2? wavelength in the continuum removed curves (Table 1).
Fig. 2. Raw spectral reflectance curves and continuum removed spectral reflectance curves of weathered granite specimens from S1 to S3.
Table 1. Maximum absorption depth in the vicinity of 2.2? wavelength
5. Conclusion
We applied reflectance spectroscopy to assess granite deterioration.
The authors appreciate the financial support from National Research Institute of Cultural Heritage (project title: Development on Evaluation Technology of Deterioration for Conservation of Stone Cultural Properties, project no: 06B001Y-00150-2006).
References
Surface Weathering Degree Mapping for Granite Using Reflectance Spectroscopy
Chang-Uk Hyun
Department of Civil, Urban and Geosystem Engineering, Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
hyuncu99@snu.ac.kr
Hyeong-Dong Park
Department of Civil, Urban and Geosystem Engineering, Seoul National University, Shillim-dong, Gwanak-gu, Seoul 151-744, Korea
hpark@snu.ac.kr
Abstract Combinations of reflectance spectroscopy and various constituents matching algorithms have been successfully used to classify and to detect geomaterials in field of remote sensing. Measuring reflectance spectra on the rock surface can be applied to assess degradation of rock surface as a new non-destructive inspection method. In this paper the spectral reflectances of weathered granite specimens of Mt. Gwanak were measured by using field spectrometer and spectral characteristics of reference minerals were used to identify rock-forming minerals of the granite from the spectral reflectances obtained using field spectrometer. Granite is mainly composed of quartz, feldspar and mica. Hardness and durability of quartz are greater than other granite forming minerals and quartz has no diagnostic peak in spectral reflectance curves, but feldspar and mica produce clay minerals, such as illite and kaolinite, according to weathering processes. Thus comparison of the amount of the clay minerals using absorption peak in the spectral reflectance curves among differently weathered granite specimens could result in newly designed weathering indices against rock surface mineral composition.
1. Introduction
In civil engineering, rocks are used for building materials and foundation of construction, so its engineering properties and physical characteristics are critical for concrete construction. Weathering changes physical characteristics of rocks, such as strength, hardness and durability, or texture and color on the surface which are important for conservation of stone monument and exterior of the building. To assess weathering degree of rocks various techniques and methods have been used. Qualitative assessments using naked eye of geologist and chemical analyses of rock-forming mineral composition have been commonly used to assess rock deterioration. But chemical analyses are time-consuming and damage objects. The assessments by geologist have limits to produce subjective and qualitative results. Reflectance spectroscopy is non-destructive and makes fast investigation on the rock surface. Spectra measured using spectrometer on the rock surface make researcher quantitative interpretation about weathering degree. In this paper we investigated weathering processes of granite forming minerals and measured reflectance curves on the weathered granite specimens of Mt. Gwanak in Korea. By using absorption features of the spectra weathering degree of specimens could be compared.
2. Weathering Characteristics of Mt. Gwanak Granite
Granite of Mt. Gwanak is biotite granite (Kwon et al., 1995). Its constituents are quartz, feldspar and mica, especially biotite. Hardness and durability of quartz are greater than other granite forming minerals and quartz has no diagnostic peak in spectral reflectance curves. Feldspar and mica produce clay minerals, such as illite and kaolinite, according to weathering processes. Spectral reflectance curves of granite constituents have no diagnostic absorption peaks except for microcline in the vicinity of 2.2? wavelength. Spectral reflectance curves of clay minerals show strong absorption peak in the vicinity of 2.2? wavelength (Clark et al., 2003).
3. Surface Weathering Degree Assessment of Granite
Field spectrometer (Fieldspec®3) was used to measure surface reflectance curves of granite specimens. The prove of 25 degree FOV (field of view) was applied to measure reflectances of three specimens and two types of target area, circles of 1cm and 2cm diameter, were set up (Fig. 1).
Fig. 1. Target areas for measurement of spectral reflectances. The diameter of big spot is about 2cm and the diameter of small spot is about 1cm.
4. Results
Spectral reflectances of weathered granite surface were measured and continuum removal step was processed (Fig. 2) to remove background absorptions and extract inherent absorption features (Clark and Roush, 1984; Kruse et al., 1985). Quantitative comparison among weathered specimens was derived using absorption feature and its depth of 2.2? wavelength in the continuum removed curves (Table 1).
Fig. 2. Raw spectral reflectance curves and continuum removed spectral reflectance curves of weathered granite specimens from S1 to S3.
5. Conclusion
We applied reflectance spectroscopy to assess granite deterioration.
- Detecting the amount of clay minerals, such as kaolinite and illite, can be used to identify weathering degree of granite.
- Clay minerals on the surface of granite can be detected and measured using absorption peak of 2.2? wavelength in the reflectance curves.
- The presence of clay minerals, the evidence of weathering, was numerically converted to absorption depth.
The authors appreciate the financial support from National Research Institute of Cultural Heritage (project title: Development on Evaluation Technology of Deterioration for Conservation of Stone Cultural Properties, project no: 06B001Y-00150-2006).
References
- Clark, R.N., and Roush, T.L., 1984, Quantitative analysis techniques for remote sensing applications, Journal of Geophysical Research, vol. 89, p.6329-6340.
- Clark, R.N., 1999, Chapter 1: Spectroscopy of Rocks and Minerals, and Principles of Spectroscopy, Manual of Remote Sensing, 3rd ed., vol. 3, Wiley, New York, p.3-58.
- Clark, R.N., Swayze, G.A., Wise, R., Livo, K.E., Hoefen, T.M., Kokaly, R.F. and Sutley, S.J., 2003, USGS Digital Spectral Library splib05a, USGS Open File Report 03-395, http://pubs.usgs.gov/of/2003/ofr-03-395/ofr-03-395.html (accessed 30 May 2006).
- Kruse, F. A., Raines, G. L., and Watson, K., 1985, Analytical techniques for extracting geologic information from multichannel airborne spectroradiometer and airborne imaging spectrometer data, Proceedings of International Symposium on Remote Sensing of Environment, Thematic Conference on Remote Sensing for Exploration Geology, 4th, Environmental Research Institute of Michigan, Ann Arbor, p309-324.
- Kwon, S.T., Shin, K.B., Park, H.K., and Mertzman, S.A., 1995, Geochemistry of the Kwanaksan alkali feldspar granite: A-type granite?, The Korean Journal of Petroleum Geology, vol. 4, p.31-48.